Biopsy taken from suspected malignant tissue inside the bronchial tree is conventionally performed using a bronchoscope. The bronchoscope, which is a type of endoscope, is a flexible tube having a miniature camera at its tip. Actuated from a handle at its proximal end, its tip has the ability to deflect in two opposite directions, allowing it to be steered inside the bronchial tree. The bronchoscope also has a working channel, typically of internal diameter about 2.8 mm, allowing a tool such as a biopsy forceps to be inserted and driven ahead of its distal tip.
Once unidentified lung mass is discovered in a CT scan, a biopsy of this mass should be taken. The patient is positioned on an operating table, a bronchoscope is inserted into the bronchial tree and directed towards the mass. Once the tip of the bronchoscope is placed in contact with the mass, as validated by direct viewing of the mass in the bronchoscope image, a forceps is pushed via the working channel into the mass and biopsy is taken.
While this technique is straightforward in principle, the practical application is often highly problematic. The air paths of the bronchial tree get progressively narrower as they branch with increasing depth into the bronchial tree. A typical bronchoscope is a two- or three-lumen structure (including fiber bundles for imaging and illumination and working channel for suction and/or tools) and is typically around 5 or 6 millimeters in diameter. In consequence, a bronchoscope can reach only the third, or at most the fourth, bifurcation level of the tree (indicated by a dashed circle in FIG. 24). If the mass is at the periphery of the tree, the biopsy forceps must be pushed further ahead of the tip of the bronchoscope in the estimated direction of the mass. The biopsy itself is then taken blindly. X-ray fluoroscopic imaging is often used as a visual aid, but this is only of any value for relatively large masses visible under a fluoroscope, and the two-dimensional images produced are a poor navigation aid, lacking depth perception. For these and other reasons, it is estimated that more than 60% of the total number of bronchial biopsies are taken mistakenly in a wrong location.
Various devices have been proposed in order to try to ameliorate the limitations of bronchoscopes. Of particular interest is U.S. Pat. No. 4,586,491 to Carpenter which discloses a bronchoscope with a small gauge viewing attachment. The viewing attachment is selectively advanced past the end of the bronchoscope to view tissue beyond the reach of the main bronchoscope shaft.
Although the device of Carpenter allows viewing of tissue within passageways too narrow for the bronchoscope to enter, it is very limited in its usefulness. Firstly, the viewing attachment is not steerable, relying instead on the pointing direction of the end of the bronchoscope. As a result, the viewing attachment is limited in its capabilities to reach target tissue. Secondly, the system provides no location information to facilitate navigation to the target tissue. Finally, the device is of little or no use for navigating a medical tool to the target location. If the viewing attachment is removed to allow introduction of a tool to the working channel, manipulation of the tool must again be performed “blindly” without any guarantee that the correct target tissue has been reached.
There is therefore a need for endoscopes and corresponding methods which facilitate navigation to a target within a branched structure such as the bronchial tree, and which allows a medical tool to be brought accurately to the target.